Oxidation of fats, vegetable oils, carotenoids and their biologically active derivatives, Vitamin A, and of essential oils and other flavorings results in degradation of their quality, and is deleterious to foodstuffs containing the oxidized products.
The art shows many methods of inhibiting lipid oxidation by adding fat-soluble antioxidants to the substrate. The art does not show the stabilization of fats, oils, fatty foods and ingredients of foods employing green tea catechins in a form effective for such purpose.
Green tea is known to contain significant amounts of four catechins. Their structures are as follows: ##STR1## In the preparation of black or fermented teas, these catechins are partially or totally oxidized as shown by Sanderson, U.S. Pat. No. 3,812,266. The oxidized catechins are much less effective antioxidants, so that green tea is the preferred source of catechins for the product of this invention.
Hara, in U.S. Pat. No. 4,840,966, describes the therapeutic use of catechins to reduce blood pressure. They are administered orally in the form of tablets or incorporated into the diet. Other health benefits of green tea catechins are known.
Catechins are very soluble in water, and many patents have issued pertaining to methods of extracting them to make instant tea. Examples of such patents include Mishkin, U.S. Pat. No. 3,451,823. He describes a method of first extracting the tea with hot water, which will recover the catechins, and then reextracting with highly superheated water under pressure, to degrade and solubilize other tea materials, which may also have antioxidant properties. These undefined substances, of unknown toxicology, are not included in the preferred form of this invention.
Mai, U.S. Pat. No. 4,839,187, describes a process for making the superheated water extract of Mishkin into a composition effective for the stabilization of lipids. His process starts with black tea, not green tea, and the superheating creates gallic acid, which he considers an important component of his extract. It is not desired in, and not created in, the product and process of this invention, since it is known to develop purple colors in the trace presence of metals. His extract is directly added to the fat to be stabilized in a solid form, or mixed with lecithin. He does not show or suggest any lecithin solution or a method of obtaining such, which are important objects of this invention.
Although water extraction of the catechins is an acceptable method of separating the catechins from the tea, polar organic solvents, such as methanol and ethanol, may be used. Hara, U.S. Pat. No. 4,673,530, describes such an extraction using aqueous alcoholic solutions. These aqueous alcoholic extracts complicate the preparation of the preferred form of catechins used in this invention, since it has been found that interfering water- soluble substances are also extracted. These interfering substances are desirably removed if an extract of Hara's type is used. The use of essentially anhydrous solvents is preferred in this invention. The separation of caffeine, which is also present in the aqueous and organic extracts, can be achieved by conventional methods as described in the Hara patent, employing chloroform, leaving the catechins in the water phase and the caffeine in the organic phase. Hara then recovers the catechins from the water using ethyl acetate, without any adjustment of pH, and this solvent is then removed to give a powder.
Alternatively, the caffeine may be removed from the tea leaves by supercritical carbon dioxide extraction, as is done in the preparation of decaffeinated tea leaves. However, the separation of caffeine from the catechins is not necessary or even preferred in this invention, since it does not interfere with the antioxidant activity of the catechins in the lipid. On the other hand, the elimination of the use of chloroform is an object of this invention.
Hara, in U.S. Pat. No. 4,613,672, describes an elegant method of preparation of purified individual catechins for use in pharmaceutical preparations. These products can be used as aqueous solutions, or as dried powders. He also shows that ethanolic solutions of these powders, when added to lipids, act as antioxidants.
Being insoluble in lipids and other non-polar solvents, concentrated solutions of catechins in vegetable oils cannot be prepared, and an aqueous solution will simply separate from the lipid to be stabilized. Ethanolic solutions are unstable in use. Likewise, dry powders do not go into solution in oil even with prolonged heating at over 100.degree. C. and agitation, and are inefficient as antioxidants.